1. Field of the Invention
The invention relates to a device for scanning a disc-shaped information carrier which is provided, near a circumference, with a support element manufactured from a magnetizable material, which device is provided with an electromagnetic system for co-operating with the support element and with a scanning unit for scanning information present on the information carrier, said information carrier, by co-operation between the electromagnetic system and the support element, being positionable with respect to the scanning unit, rotatable about an axis of rotation directed perpendicularly to the information carrier and displaceable along an X-axis directed perpendicularly to the axis of rotation.
The invention also relates to a disc-shaped information carrier which is provided, near a circumference, with a support element manufactured from a magnetizable material, which support element is used to co-operate with a device in accordance with the invention.
2. Description of the Related Art
A device and a disc-shaped information carrier of the types mentioned in the opening paragraphs are disclosed in EP-A-0 300 336. The known information carrier is provided, along its circumference, with a ring of a ferromagnetic material for co-operating with the electromagnetic system of the known device. The scanning unit of the known device is secured, in a fixed position, to a frame of the device. The scanning unit includes a read and write head by means of which information present on the information carrier can be read or information can be written on the information carrier. The electromagnetic system of the known device comprises two pairs of rows of electromagnets. Viewed in a middle position of the information carrier along the X-axis and viewed in a direction parallel to a Y-axis extending perpendicularly to the axis of rotation and the X-axis, both pairs are arranged diametrically opposite each other, the ferromagnetic ring of the information carrier being situated, in operation, approximately between the two rows of electromagnets of each pair. Furthermore, said ring is situated, in operation, between the electromagnets of eight pairs of electromagnets which are arranged between the two pairs of rows of electromagnets so as to be distributed along the circumference of the information carrier. The electromagnets of said rows and pairs exert, in operation, electromagnetic forces on the ring of the information carrier. The known device further comprises a system of sensors by means of which a position of the information carrier with respect to the frame and the scanning unit can be measured, and the known device further comprises a control unit by means of which the electromagnetic forces can be controlled such that the measured position of the information carrier with respect to the scanning unit substantially corresponds to a desired position. In operation, electromagnetic forces are used to position the information carrier, with respect to the scanning unit, in five degrees of freedom, i.e. in all degrees of freedom except the degree of freedom about the axis of rotation. In operation, the electromagnetic forces are controlled such that the information carrier is rotated about the axis of rotation and simultaneously displaced along the X-axis in such a manner that the scanning unit follows a spiral-shaped information track present on the information carrier. The construction of the known device thus is very simple compared to that of conventional devices for scanning disc-shaped information carriers, which are provided with a rotatable turntable for the information carrier and with a displacement device for displacing and positioning the scanning unit with respect to the rotating information carrier.
A drawback of the known device resides in that the applied electromagnetic system has a large number of electromagnets. As a result, the construction of the electromagnetic system and the necessary control unit are complicated.
It is an object of the invention to provide a device of the type mentioned in the opening paragraphs, which is provided with an electromagnetic system enabling an information carrier of the type mentioned in the opening paragraphs to be positioned also in five degrees of freedom with respect to the scanning unit, i.e. all degrees of freedom except the degree of freedom about the axis of rotation, but the construction of said electromagnetic system being simplified.
To achieve this object, a device in accordance with the invention is characterized in that the electromagnetic system is provided with a single pair of rows of electromagnets arranged along the X-axis, said rows of electromagnets, viewed in a direction parallel to the axis of rotation, being arranged on either side of the information carrier, and with a first pair of electromagnets and a second pair of electromagnets which, viewed in a middle position of the information carrier along the X-axis and viewed in a direction parallel to a Y-axis extending perpendicularly to the axis of rotation and the X-axis, are arranged substantially diametrically opposite each other, the electromagnets of each pair, viewed in a direction parallel to the X-axis, (Marc, tekst claim 1 wijkt hier af) being arranged on either side of the information carrier, and the magnetic poles of the electromagnets being at substantially the same distances from the axis of rotation (ook hier wijkt tekst af van claim 1) and, in each position of the information carrier along the X-axis, on one side of a magnetic point of application of the support element.
It is to be noted that the expression xe2x80x9cmagnetic point of applicationxe2x80x9d is to be taken to mean a point at which the electromagnetic force of an electromagnet of the electromagnetic system acts on the support element. As the two pairs are substantially diametrically arranged with respect to each other and the poles of the electromagnets of the two pairs are at substantially equal distances from the X-axis and are situated, in each position of the information carrier along the X-axis, at one side of the magnetic point of application, the electromagnetic forces of the two pairs comprise, in each position of the information carrier along the X-axis, both a component parallel to the axis of rotation and a component along the Y-axis, the components along the Y-axis of the two pairs extending in opposite directions. As the rows of electromagnets extend along the X-axis, in each position of the information carrier along the X-axis, at least one pair of electromagnets of both rows are situated in positions on either side of the magnetic point of application. The electromagnetic forces of the relevant pairs comprise a component extending parallel to the axis of rotation as well as a component extending along the X-axis, the components extending along the X-axis of the electromagnets of each of the relevant pairs extending in opposite directions. The position of the information carrier along the Y-axis can be controlled by controlling said oppositely directed components along the Y-axis of the forces of the first and the second pair by means of a control unit and a system of position sensors. The position of the information carrier along the X-axis can be controlled by controlling said oppositely directed components along the X-axis of the forces of the pair of rows. By controlling said components, directed parallel to the axis of rotation, of the forces of the two pairs and of the pair of rows, both the position of the information carrier parallel to the axis of rotation and the angles of the information carrier about the X-axis and Y-axis can be controlled. As the electromagnetic system comprises only a single pair of rows of electromagnets and two pairs of diametrically arranged electromagnets, the construction of the electromagnetic system is comparatively simple, and the number of electromagnets to be controlled is limited, so that also the necessary control unit is comparatively simple.
A particular embodiment of a device in accordance with the invention is characterized in that the magnetic poles of the electromagnets of the two rows, viewed in a plane wherein the axis of rotation and the X-axis are situated, are arranged in a zigzag pattern. By virtue thereof, it is achieved that, in each position of the information carrier along the X-axis, at least one pair of juxtaposed electromagnets of at least one of the two rows are situated in positions on either side of the magnetic point of application of the support element. Besides, in each position of the information carrier along the X-axis, the largest possible concentration of electromagnets around the support element is achieved. As a result, optimum use is made of the electromagnets of the two rows, and the number of necessary electromagnets of the two rows is limited.
A further embodiment of a device in accordance with the invention is characterized in that the magnetic poles of the electromagnets of the first and the second pair are situated, in each position of the information carrier along the X-axis, at a larger distance from the X-axis than the magnetic point of application of the support element. By virtue thereof, it is achieved that the magnetic poles of the electromagnets of the two pairs are situated, taking the average of all positions of the information carrier along the X-axis, at a comparatively small distance, parallel to the Y-axis, from the magnetic point of application. As a result, the components directed parallel to the axis of rotation of the electromagnetic forces of the electromagnets of the two pairs, taking the average of all positions of the information carrier along the X-axis, are comparatively large, so that these electromagnets exert a comparatively large supporting force on the information carrier in a direction parallel to the axis of rotation.
Yet another embodiment of a device in accordance with the invention is characterized in that the electromagnets of the first and the second pair are each provided with a U-shaped core and an electric coil wound about a core base extending substantially parallel to the X-axis, the magnetic poles being formed by end portions of two legs of the core, which legs extend substantially parallel to the axis of rotation and are directed towards the other electromagnet of the relevant pair. As said base of the core extends parallel to the X-axis, the two magnetic poles of the electromagnets of each pair are situated at substantially equal distances from the X-axis. As a result, it is achieved that, in each position of the information carrier along the X-axis, the two magnetic poles are situated at the smallest possible distance from the magnetic point of application of the support element, so that the supporting force exerted by the electromagnets of the two pairs on the information carrier in a direction parallel to the axis of rotation is as large as possible.
A particular embodiment of a device in accordance with the invention is characterized in that the electromagnets of each row are provided with a U-shaped core and an electric coil wound about a core base extending substantially parallel to the Y-axis, the magnetic poles being formed by end portions of two legs of the core, which legs extend substantially parallel to the axis of rotation and are directed towards the other row. As said base of the core extends parallel to the Y-axis, the two magnetic poles of the electromagnets of each row are situated at substantially equal distances from the Y-axis. By virtue thereof, it is achieved that the two magnetic poles are situated, in each position of the information carrier along the X-axis, at the smallest possible distance from the magnetic point of application of the support element, as a result of which the supporting force exerted by the electromagnets of the two rows on the information carrier in a direction parallel to the axis of rotation is as large as possible.
A further embodiment of a device in accordance with the invention is characterized in that between the first pair and the second pair of electromagnets, there is a distance which is larger than approximately 4 mm and smaller than approximately 40 mm.
A disc-shaped information carrier in accordance with the invention, which can suitably be used to co-operate with the above-mentioned further embodiment of a device in accordance with the invention is characterized in that the information carrier has a diameter which is larger than approximately 4 mm and smaller than approximately 40 mm.
Apart from the scanning unit, the device in accordance with the invention, in principle, only comprises the electromagnetic system and the necessary control unit, as a result of which the device can very suitably be miniaturized. In said further embodiment, the necessary dimensions of the device are limited such that the device can suitably be provided in very small spaces, such as comparatively small pockets in articles of clothing or bags. It has been found that, at a diameter of the information carrier above approximately 4 mm and below approximately 40 mm, a particularly stable support of the information carrier by means of the electromagnetic system of the device in accordance with the invention is achieved.
A still further embodiment of a device in accordance with the invention is characterized in that the device can suitably be used for scanning a disc-shaped information carrier whose support element, viewed in a radial direction with respect to the axis of rotation, has a width which varies in the circumferential direction between a minimum value and a maximum value, a substantially constant pitch being present between successive positions where the width has said maximum value, in which device the magnetic poles of at least one electromagnet of at least one of the two pairs or the magnetic poles of each electromagnet of at least one of the two rows are mutually arranged in a substantially tangential direction with respect to the axis of rotation, a pitch which is substantially equal to said pitch of the support element being present between said magnetic poles.
A disc-shaped information carrier in accordance with the invention, which can suitably be used to co-operate with the above-mentioned still further embodiment of a device in accordance with the invention is characterized in that the support element, viewed in a radial direction with respect to the axis of rotation, has a width which varies in the circumferential direction between a minimum value and a maximum value, a substantially constant pitch being present between successive positions where the width has said maximum value.
As the pitch between said magnetic poles is substantially equal to said pitch of the support element, said magnetic poles are capable of exerting an electromagnetic force on the support element, in a substantial part of all possible angular positions of the information carrier about the axis of rotation, which electromagnetic force includes a component in said tangential direction. Under the influence of said component of the electromagnet force, the information carrier is rotated about the axis of rotation. A continuous rotation of the information carrier about the axis of rotation at a desired speed of rotation is achieved by controlling said electromagnets in a suitable manner by means of the control unit.
A particular embodiment of a disc-shaped information carrier in accordance with the invention is characterized in that the support element has at least one undulated edge. As the support element has an undulated edge, it is achieved, in a practical manner, that the support element, viewed in a radial direction with respect to the axis of rotation, has a width which varies in the circumferential direction between a minimum value and a maximum value.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.